Abrasive-jet cutting systems are used for cutting a wide variety of materials and for the production of a wide variety of products. In a typical abrasive-jet cutting system, abrasive particles are mixed with an ultra-high pressure fluid (e.g., water), and the resulting ultra-high pressure abrasive fluid is flowed through a cutting nozzle which directs an abrasive cutting jet onto a workpiece. The cutting nozzle may then be controllably moved across the workpiece to cut the workpiece into the desired shape. After the ultra-high pressure abrasive jet passes through the workpiece, the energy of the abrasive jet is dissipated and the abrasive fluid is collected in a catcher tank for disposal. Abrasive-jet cutting systems of this type are shown and described, for example, in U.S. Pat. No. 5,643,058 issued to Erichsen et al. and assigned to Flow International Corp. of Kent, Washington, which patent is incorporated herein by reference, corresponding to Flow's Bengal 4.times.4 and Paser 3 abrasive-jet cutting systems.
One abrasive material commonly used in abrasive-jet cutting systems is garnet. Garnet is well known for its hardness, resiliency, and overall performance in abrasive-jet cutting systems for a wide variety of workpiece materials. The cost of garnet, however, is not insubstantial. In existing abrasive-jet cutting systems, the consumable garnet particles represent 60 to 75 percent of the operating costs of the system. Research into the recovery and recycling of garnet particles indicates, however, that between 40 and 60 percent of the garnet particles are typically large enough to be recovered and recycled after initial use depending upon the material properties of the workpiece being cut. This fact makes abrasive recycling commercially viable.
Currently, abrasive recovery apparatus for use with abrasive-jet cutting systems may be divided into two broad categories. In a first category, the abrasive-laden fluid contained within the jet catcher of the abrasive jet cutting system is simply removed to a heater and subjected to heat to evaporate the fluid, leaving a mixture of abrasive particles and cuttings (or "fines") from the workpiece. This mixture of abrasive particles and cuttings is then sifted, such as through a system of successive screens, to remove the desirable abrasive particles from the undesirable cuttings and unusable particles.
In a second category, the abrasive-laden fluid is removed from the jet catcher and is separated by a wet separation process known as "classification" into a low-concentration abrasive flow and a wet recovered abrasive. The wet recovered abrasive is then heated to evaporate the fluid, leaving a mixture of dry recovered abrasive and cuttings for segregation. The low-concentration abrasive flow may simply be disposed of, or may be transported to a fine-separation tank to allow the fine particulates to settle and be recovered. In this second category of abrasive recovery systems, energy savings may be achieved because the low-concentration abrasive flow is not heated, with correspondingly lower operational costs. An abrasive recycling system of this type is shown and described, for example, in DE 19645142 issued to Hering et al. and assigned to Intrec Ges Innovative Technologien MbH of Berlin, Germany, which patent is incorporated herein by reference.
FIG. 1 is a schematic view of an existing abrasive recovery apparatus 10 of the type that uses classification. First, an abrasive-laden fluid 22 is pumped through the cutting head 12 to form an abrasive jet 14. The abrasive jet 14 is passed through a workpiece and collected in a catcher tank 16. A pump 18 draws the abrasive-laden fluid 22 from the catcher tank 16 and pumps it through a bypass 20 to a hydro-classifier 34.
The abrasive-laden fluid 22 enters into an upper portion 36 of a hydro-classifier 34. A clear-fluid pump 38 draws a clarified fluid 30 from a reserve tank 32 and pumps it into a lower portion 40 of the hydro-classifier 34. The abrasive-laden fluid 22 passes downwardly through a middle portion 42 of the hydro-classifier 34, while the clarified fluid 30 passes upwardly through the middle portion 42. The resulting mixing in the middle portion 42 of the hydro-classifier 34 causes the abrasive-laden fluid 22 to separate into a recovered abrasive 44 and a fine-particle flow 46. The recovered abrasive 44 collects in the bottom portion 40 of the hydro-classifier 34. The fine-particle flow 46 is routed to a clearing tank 26 for separation as described below.
The recovered abrasive 44 exits from the hydro-classifier 34 to a wet abrasive storage receptacle 47. If the wet abrasive storage receptacle 47 becomes filled to capacity, the bypass 20 directs the abrasive-laden fluid 22 directly to the clearing tank 26. An auger 48 transports the recovered abrasive 44 from the wet abrasive storage receptacle 47 to a dryer 50. In the dryer 50, the recovered abrasive 44 is heated to remove any remaining moisture, and is shaken and sifted through screens to separate the recovered abrasive 44 from any non-reusable particulates. The recovered abrasive 44 is then deposited into a collection tank 52 for reuse in the abrasive jet cutting system.
The fine-particle flow 46 is shunted to the clearing tank 26 where the particles are permitted to settle to the bottom. A sediment 27 which collects at the bottom of the clearing tank 26 includes cuttings from the workpiece as well as fine, non-reusable abrasive particulates. The sediment 27 is collected in a receptacle 28 for disposal or subsequent processing. Clarified fluid 30 exits from the settling tank 26 and is collected in the reserve tank 31. From the reserve tank 31, the clarified fluid 30 may be pumped by a filter pump 32 through a filter 33 and into a waste disposal system (not shown). Alternately, the clarified fluid 30 may be pumped by a return pump 35 from the reserve tank 31 back to the catcher tank 16 as necessary.
Although desirable results may be achieved using the abrasive recovery apparatus 10, certain characteristics may be improved. For example, the energy costs associated with the dryer 50 remain high and the throughput of the dryer 50 is low. Furthermore, the hydro-classifier 34 is typically extremely large. These characteristics tend to make the abrasive recovery apparatus 10 economically non-viable and it is impractical for most cutting environments.